Journal of Animal Science · 1971 · 79 citations · 0 references
Veterinary MedicineAnimal SciencesEndocrinologyNeuroendocrinologyReproductive EndocrinologyReproductive PhysiologyHormonal Regulation Of ReproductionPituitary HormonesRuminant EndocrinologySheep PhysiologySheep ReproductionEstrous Cycle PhasesEstrous Cycle RegulationEstrus BehaviorFemale Reproductive PhysiologyHormonal Assays In RuminantsSurge
Three mature, whitefaced ewes were used to study the responses to purified porcine LH-RH at various stages of the estrous cycle. The estrus activity of the ewes was checked twice daily with a vasectomized ram. Each ewe received 3 µg LH-RH dissolved in 5 ml saline intracarotidly. Venous blood samples were collected prior to and after administration of LH-RH. Serum LH levels in the samples were quantitated by a double antibody radioimmunoassay. The present experiments show that after administration of LH-RH an elevation of serum LH occurs at all stages of the estrous cycle. The same dose of LH-RH induced a greater change in serum LH during an 8±4-hr. period on day 1 than at any other stage of the estrous cycle. Thus, present evidence indicates that pituitary responsiveness to LH-RH at estrus is considerably greater than at other stages of the estrous cycle, and may be an important factor in the preovulatory surge of LH.